1. Field of the Invention
This invention relates to an air-fuel ratio control device for internal combustion engines whereby airflow is supplied into the fuel-air mixture fed into the engine from the carburetor so that the mixture will have precisely the theoretical air-fuel ratio to purify the exhaust gas.
2. Description of the Prior Art
Presently, catalytic converters are popularly used for purification of exhaust gas released from the internal combustion engines. Exhaust gas purifying efficiency of such catalytic converters, however, is greatly affected by the air-fuel ratio in the engine. For constantly maintaining high purifying efficiency of the catalytic converters, it is desirable that the air-fuel ratio characteristic of the carburetor be controlled with extremely high accuracy.
Generally, the carburetor used in an internal combustion engine is capable of feeding a fuel-air mixture having a substantially constant air-fuel ratio characteristic in all modes of engine operations. However, if examined minutely, such air-fuel ratio is found to vary within the range of about 20% according to engine speed and load condition, and hence a correct air-fuel mixture is not always supplied to the engine, thus often causing imperfect purification of exhaust gas.